1. Field of the Invention
The present invention relates to a sync separation circuit that separates a synchronizing signal from a video signal containing the synchronizing signal.
2. Description of the Related Art
Various video signal processing apparatuses, such as TV receivers and video players, conventionally separate a synchronizing signal from an input video signal and utilize the separated synchronizing signal to execute a process such as reproduction. The synchronizing signal is combined into the video signal during horizontal or vertical blanking intervals as a low-level signal. Then, the video signal is normally compared with a threshold value of a predetermined level, and a part of the video signal which is at a level equal to or lower than the predetermined one is then extracted. The synchronizing signal is thus separated.
The video signal has a sync tip level indicating the level of the bottom of the synchronizing signal, and a pedestal level that is the level of a porch portion on which a color burst signal is superimposed. To allow the video signal to be sliced to obtain the synchronizing signal, an intermediate level between the sync tip level and the pedestal level is often set to be a slice level.
Japanese Patent Laid-Open Publication No. Hei 11-220634 is a document relating to the above-described process.
When the intermediate level between the sync tip level and the pedestal level is set to be the slice level as described above, if a reproduction signal level of a video varies significantly during video reproduction or a reception signal level of a TV signal varies significantly owing to a weak electric field, sync separation may not always be achieved properly.